brother, tamerlan, killed in a gun battle early friday morning while wearing explosives strapped to his chest, may have instigated the plot and persuaded dzhokhar to join him, but why? the brothers originally from chechnya, were raised in the u.s., living in the same house, and seemed to fit in. both were athletic. dzhokhar, a wrestler, and tamerlan, a boxer. who hoped to be on the u.s. olympic team. but in recent years, tamerlan had changed and became radicalized, according to his uncle, who says he then spoke to a family friend. >> he said there is someone who brainwashed him, some newly convert to islam. >> reporter: in 2011, russian intelligence, concerned about the threat of chech knowian terrorism asked the fbi to investigate tamerlan, based on information that he was a follower of radical islam and that he had changed drastically since 2010, according to an fbi statement. the fbi says a checked databases, interviewed tamerlan and family members, but quote did not find any terrorism activity, domestic or foreign. the fbi says it asked the russians for more, but never got answers.